I was looking for something like this for long time,, cool project,
What about restructuring entities to follow some polymorphisms for hardware devices sensors and actuators ,, and software utilities like delay... Etc

Here are some ideas for future improvement of this library:

• Improve GPIO class
• Improve DC Motor class
• Add differential mobile robot class

Feel free to suggest yours

In the line 79 of GPIO.cpp there are a double condition similar.

int GPIO::read(Pin& pin){
    if (pin.port() == PortB) {
        return (*pinb & (1 << pin.pin())) ? 1 : 0;
    }else if(pin.port() == PortB){
        return (*pind & (1 << pin.pin())) ? 1 : 0;
    }

    return GPIO::analogRead(pin.pin());
}

I suppose that in the second if, is pin.port() == PortD.

GPIO.cpp

Hi!

You should not cast millis - this->_previous to int.
It's better to change threshold to unsigned long and do all math without casting.